# Nucleosome interaction of the CPC secures centromeric chromatin integrity and chromosome segregation fidelity

## TL;DR

The CPC complex helps ensure accurate chromosome segregation by stabilizing centromeric chromatin through direct interactions with nucleosomes.

## Contribution

The study reveals a non-catalytic role of CPC in chromatin stabilization via nucleosome interactions.

## Key findings

- CPC engages with nucleosome acidic patch and DNA entry-exit site via Borealin and INCENP.
- CPC-nucleosome binding protects chromatin from MNase digestion and ensures error-free chromosome segregation.
- Disrupting CPC-nucleosome interactions leads to chromosome segregation errors and altered kinetochore stretch.

## Abstract

The chromosomal passenger complex (CPC; Borealin-Survivin-INCENP-Aurora B kinase) ensures accurate chromosome segregation by orchestrating sister chromatid cohesion, error correction of kinetochore-microtubule attachments, and spindle assembly checkpoint signaling. Correct spatiotemporal regulation of CPC is critical for its function. Phosphorylations of histone H3 Thr3 and histone H2A Thr120 and modification-independent nucleosome interactions involving Survivin and Borealin contribute to CPC centromere enrichment. However, how various nucleosome binding elements collectively contribute to CPC centromere enrichment at the mechanistic level, and whether CPC has any non-catalytic role at centromere remain open questions. Combining the high-resolution cryo-EM structure of a CPC-bound H3Thr3ph nucleosome with atomic force microscopy and biochemical and cellular assays, we demonstrate that CPC employs multipartite interactions, which facilitate its engagement with nucleosome acidic patch and the DNA entry-exit site. Perturbing the CPC-nucleosome interaction compromises chromatin protection against MNase digestion in vitro, and centromeric chromatin stability and error-free chromosome segregation in cells. Our work suggests a non-catalytic chromatin-stabilizing role of CPC in maintaining centromeric chromatin features critical for kinetochore function.

Correct spatiotemporal regulation ensures accurate function of the chromosomal passenger complex (CPC) in chromosome segregation fidelity. Here, structural, biochemical, and cellular data suggest an additional non-catalytic CPC role in stabilizing centromeric chromatin via direct nucleosome interactions.

Cryo-EM reveals CPC engagement with the nucleosome acidic patch and the DNA entry-exit site, mediated by the N-terminal tail and downstream α-helix of Borealin, respectively.Intrinsically-disordered regions of Borealin (Borealin loop) and INCENP (RRKKRR motif) contribute to CPC-nucleosome binding through conformationally heterogeneous interactions with histones and nucleosomal DNA.CPC-nucleosome binding stabilizes DNA wrapping of the nucleosome and protects nucleosomal DNA of a chromatin array and centromeric chromatin from digestion by MNase activity in vitro and in cells, respectively.Perturbing the CPC-nucleosome interaction abolishes the MNase protection ability of the CPC, leading to altered inter-kinetochore stretch during metaphase and to chromosome segregation errors.

Cryo-EM reveals CPC engagement with the nucleosome acidic patch and the DNA entry-exit site, mediated by the N-terminal tail and downstream α-helix of Borealin, respectively.

Intrinsically-disordered regions of Borealin (Borealin loop) and INCENP (RRKKRR motif) contribute to CPC-nucleosome binding through conformationally heterogeneous interactions with histones and nucleosomal DNA.

CPC-nucleosome binding stabilizes DNA wrapping of the nucleosome and protects nucleosomal DNA of a chromatin array and centromeric chromatin from digestion by MNase activity in vitro and in cells, respectively.

Perturbing the CPC-nucleosome interaction abolishes the MNase protection ability of the CPC, leading to altered inter-kinetochore stretch during metaphase and to chromosome segregation errors.

Cryo-EM, biochemical and cellular data suggest an additional non-catalytic role for the chromosomal passenger complex mediated by multipartite interactions with the nucleosome’s acidic patch and DNA entry-exit site.